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Radiation therapy
Radiation therapy is typically used for rectal cancer and not for colon cancer. It kills cancer cells by bombarding them with high-energy X-rays. In external beam radiation therapy, a machine sends the X-rays through the skin to the diseased part of the rectum. Or a device may be inserted directly into the rectum to treat tumors; this procedure is called endocavitary therapy. Much less widely used in colorectal cancer is brachytherapy, a form of internal radiation therapy, where radioactive seeds are left in the affected area to treat the tumor.
Combining radiation therapy and chemotherapy after surgery is currently the standard of care for patients with Stage II or III rectal cancers. Patients with recurrent or advanced disease generally are offered radiation therapy to relieve symptoms and ease pain caused by the disease. In many cases, bulky primary cancers that can't be removed can be successfully controlled for a time with radiation therapy. Cancers that have spread from the rectum to the bone, brain, or pelvis have also been successfully controlled with radiation therapy.
In rectal cancer, combined radiation therapy and chemotherapy are increasingly being given pre-operatively to patients whose cancers have spread beyond the colon wall or to lymph nodes. This one-two punch often shrinks tumors, which gives surgeons a better shot at preserving the sphincter and, thus, bowel function.
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